Control system

ABSTRACT

A control system for an air cylinder in which electronic links are used to control a cylinder from a remote location without the delay normally encountered with air transmission lines. Inlet and exhaust valves are electronically activated in response to a pressure measuring device on the air cylinder which produces a voltage signal which signal is compared to a voltage signal generated at the control location.

United States Patent [191 Kiszewski Jan. 1,1974

[52] US. Cl 91/433, 91/459, 91/454 [51] Int. Cl. FlSb 11/10, F15b 13/04, Fl5b 13/044 [58] Field of Search 91/361, 362, 363,

91/433, 454, 457, 459; 307/252 H, 259 J; 340/242, 248 A; 328/146, 147

3,223,912 12/1965 Sheheen 307/252 H 2,615,658 10/1962 Young 3,513,400 5/1970 Russell 3,125,856 3/1964 Branson et a1 91/433 Primary Examiner-Martin P. Schwadron Assistant ExaminerA. M. Zupcic Attorney-Robert M. Dunning [5 7] ABSTRACT A control system for an air cylinder in which electronic links are used to control a cylinder from a remote location without the delay normally encountered with air transmission lines. Inlet and exhaust valves are [56] References Cited electronically activated in response to a pressure mea- UNITED STATES PATENTS suring device on the air cylinder which produces a voltage signal which signal is compared to a voltage x g g signal generated at the control location. 3:641:546 2/1972 Blackburn 340/248 A 2 Claims, 1 Drawing Figure /6 E V SOURCE 26 T E VOLTAGE EXHAUST 751, s UPPLY VA WE I CONTROL SYSTEM BACKGROUND OF THE INVENTION The field of this invention encompasses generally all devices in which pressurized air is used to perform some type of work. For example, the invention is shown as controlling an air cylinder which can be used in generating force for lifting or in applying air brakes. In the prior art if it is desired to control air cylinders from a relatively remote position time delay problems are encountered. For example, in one embodiment tested having typical operating pressures whenever distances of approximately 200 feet or more were employed the time necessary to fill all of the control lines to the desired pressure so that the air cylinders could be pressurized became too long for efficient operation. Delays of from 5 to lOseconds were experienced between the time the control valve is activated and the air cylinder actually responded. Such a delay is much too long to anticipate correctly and as a result the air cylinder may be activated too soon or too late causing badly timed braking, lifting or other functions.

SUMMARY OF THE INVENTION The present invention avoids the above mentioned problems by eliminating the air lines from the controlling station to the device being controlled and substituting therefor electronic links which are instantaneous and have no time delay. Electronically controlled solenoid valves control the entrance and exit of air to the air cylinder. These valves are designed to respond to signals produced by a potentiometer at the remote control station. A pressure measuring device connected in the air cylinder line operates a second potentiometer whose voltage is compared to the controlling potentiometer, by means of operational amplifiers and silicon controlled rectifiers which in turn activate either the inlet or exhaust valve so as to increase or decrease the pressure in the air cylinder. Depending upon the flow rate of the solenoid valves the time delay can be reduced to a minimum and even virtually eliminated thus permitting extremely accurate control of the air cylinder. A further additional advantage to the present control system is that any air leaks in the air cylinder are automatically compensated for by the electronic sys tem which continuously monitors the pressure in the air cylinder relative to the desired air pressure. Therefore it may be seen that it is an object of my invention to provide a much improved control system for an air cylinder in which the air cylinder may be operated remotely without a consequent time delay. Further objects and advantages will become apparent upon consideration of the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows schematically the control system of the present invention and includes both the pressurized air connections and the electronic circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing an air cylinder is shown as the controlled element although it should be understood that this control system may be applied to many varieties of devices in which the pressure of air is to be controlled from a remote location. Likewise other fluid control systems of a hydraulic nature or the like may also suitably employ the principles of my invention. Air cylinder 10 which may control a brake or a lifting mechanism or other driving means is activated by an air pressure source 12. The amount of air admitted to air cylinder 10 is controlled by an inlet valve 14 which may comprise any of a variety of solenoid operated valves well known to those skilled in the art. An exhaust valve 16 is connected to air cylinder 10 so as to allow air to escape from cylinder 10 in response to a suitable signal. Exhaust valve 16 may also comprise a solenoid operated valve which opens by an amount proportional to the voltage signal presented to it. The pressure in air cylinder 10 is continuously monitored by an air pres sure measuring device 18. Pressure measuring device 18 is connected by a suitable mechanical connection, shown as a dashed line 20, to a potentiometer 22 so that the pressure in cylinder 10 varies the output voltage of potentiometer 22 proportionately. Air pressure measuring devices comprising elements 18, 20 and 22 are also well known to those skilled in the art and com mercially available.

The remote controlling station is shown schematically as a control lever 25 connected by a suitable mechanical connection 23 to a potentiometer 24. The degree of activation of air cylinder 10 is remotely chosen by selecting an output voltage on potentiometer 24. A voltage supply 26 is connected to both potentiometers 22 and 24 as shown in the drawing. However, a variable resistor 40 is connected between voltage supply 26 and potentiometer 22 so as to permanently bias potentiometer 22 to a slightly elevated level for reasons which will be described more fully later. The output voltage of potentiometer 22 is presented by means of a line 31 to a pair of operational amplifiers 28 and 30. The output voltage from potentiometer 24 is presented by means of a line 29 to operational amplifiers 28 and 30. To increase the air pressure in cylinder 10 control arm 25 is simply moved so as to increase the output voltage of potentiometer 24 relative to potentiometer 22. This voltage difference is sensed by operational amplifier 30 which signals a silicon controlled rectifier 34 which in turn operates inlet valve 14 so as to admit more air to cylinder 10. As the pressure rises the output voltage from potentiometer 22 also rises until the difference in voltage signals to operational amplifier 30 again becomes less than the threshold voltage of amplifier 30. At that point inlet valve 14 which is spring controlled is accordingly allowed to close by the deactivation of silicon controlled rectifier 34. A diode 38 prevents operational amplifier 30 from producing any signals in response to opposite polarity voltage differences. These opposite polarity voltage differences are produced when the output voltage from potentiometer 24 is caused to be below that of potentiometer 22 as, for example, when it is desired to reduce the pressure in air cylinder 10. These differences are detected by operational amplifier 28 which controls a silicon controlled rectifier 32 so as to operate exhaust valve 16 thus lowering the pressure in cylinder 10. Once again, as the pressure is reduced the voltage from potentiometer 22 also decreases until no signal difference is presented to operational amplifier 28 and exhaust valve 16 is therefor inactivated. A diode 36 protects amplifier 28 from responding to voltage differences corresponding to increase pressure signals.

Since all amplifying systems have a certain threshold voltage required to operate them it has been found that the pressure in cylinder can be reduced to a point where the output voltage of potentiometer 22 is below that necessary to trigger operational amplifier 30. However, some small pressure still remains in cylinder 10. In order to permit cylinder 10 to be completely evacuated a variable resistance 40 is used to bias potentiometer 22 sufficiently so that operational amplifier 28 always receives a sufficient signal to hold exhaust valve 16 open even though the output of potentiometer 22 approaches zero as the pressure in cylinder 10 approaches zero. Clearly, many other modifications may be made to the present invention without departing from its spirit and scope. For example, several types of amplifying systems may be used and in the preferred embodiment it is contemplated that operational amplifiers 28 and 30 would actually comprise several stages of amplification. Potentiometers 22 and 24 could of course be replaced by transformers or the like and the particular type of control valves used are not intended to be limiting. Consequently, the following claims are presented to cover the invention in its proper scope.

l claim: 1. An air cylinder control system comprising in combination:

a source of pressurized air; adjustable inlet valve means connected to said source and operable to admit air to the air cylinder in controlled amounts; adjustable exhaust valve means connected to allow the escape of air from said air cylinder in controlled amounts; pressure measuring means connected to said air cylinder; first electronic control means comprising a potentiometer remotely situated from said air cylinder operable to produce a voltage signal of magnitude proportional to the desired air pressure in said cylindcr;

second electronic control means comprising a potentiometer connected to said pressure measuring means so as to produce a voltage signal of magnitude proportional to the actual air pressure in said cylinder;

first amplifying means comprising operational amplifier circuits driving silicon controlled rectifier circuits connected between said first and second electronic control means to produce a signal indicative of the difference in voltage therebetween and further connected to adjust said inlet valve means in proportion to said difference in voltage magnitude;

second amplifying means comprising operational amplifier circuits driving silicon controlled rectifier circuits connected between said first and second electronic control means in opposite polarity to said first amplifying means to produce a signal indicative of the opposite polarity voltage difference therebetween and further connected to adjust said exhaust valve means in proportion to the opposite polarity difference in voltage;

diodes between said control means and said amplifying means to insure that said first and second amplifying means respond only to voltage differences of the prescribed polarity and are never activated simultaneously; and

a bias resistance connected to said second electronic control means so as to insure that said second control means always presents a signal to said second amplifying means of magnitude at least as large as the electronic threshold voltage necessary to activate said second amplifying means.

2. The apparatus of claim 1 in which said adjustable valve means comprise solenoid operated air valves operable to open in an amount proportional to the voltage signal presented to the solenoids. 

1. An air cylinder control system comprising in combination: a source of pressurized air; adjustable inlet valve means connected to said source and operable to admit air to the air cylinder in controlled amounts; adjustable exhaust valve means connected to allow the escape of air from said air cylinder in controlled amounts; pressure measuring means connected to said air cylinder; first electronic control means comprising a potentiometer remotely situated from said air cylinder operable to produce a voltage signal of magnitude proportional to the desired air pressure in said cylinder; second electronic control means comprising a potentiometer connected to said pressure measuring means so as to produce a voltage signal of magnitude proportional to the actual air pressure in said cylinder; first amplifying means comprising operational amplifier circuits driving silicon controlled rectifier circuits connected between said first and second electronic control means to produce a signal indicative of the difference in voltage therebetween and further connected to adjust said inlet valve means in proportion to said difference in voltage magnitude; second amplifying means comprising operational amplifier circuits driving silicon controlled rectifier circuits connected between said first and second electronic control means in opposite polarity to said first amplifying means to produce a signal indicative of the opposite polarity voltage difference therebetween and further connected to adjust said exhaust valve means in proportion to the opposite polarity difference in voltage; diodes between said control means and said amplifying means to insure that said first and second amplifying means respond only to voltage differences of the prescribed polarity and are never activated simultaneously; and a bias resistance connected to said second electronic control means so as to insure that said second control means always presents a signal to said second amplifying means of magnitude at least as large as the electronic threshold voltage necessary to activate said second amplifying means.
 2. The apparatus of claim 1 in which said adjustable valve means comprise solenoid operated air valves operable to open in an amount proportional to the voltage signal presented to the solenoids. 